Powder matullargy MS ppt.pptx mechanical engineering

powder metallurgy ppt for mechanical engineering

1. Powder Metallurgy

2. Introduction science of producing metal or metallic powders, and using them to make finished or semi-finished products Overview - In this process we make powder of metals , mixes it with some lubricants or additives then the mixture is compacted followed by sintering. Some secondary operations can also be carried out, if necessary.

3. Steps in Powder Metallurgy

4. Why Powder Metallurgy? Melting point of the metal to be used for making a product is too high ( eg - W, Mo) Reaction occurs at melting of certain metals Used for metals that are too hard to machine Used when very large quantity is expected

5. Powder Metallurgy Process

6. Metal Powders M etal powders are highly engineered materials Important Aspects of metal powders : the particle size, the distribution and shape of the metal powder affect the properties of the compacted product the particle size is usually measured by screening Passing the metal powder through sieves of various mesh sizes Larger the mesh size, smaller is the opening in the sieve The distribution of the particle size is given in terms of frequency distribution plot, the maximum is called the Mode Size The particle shape is described in terms of the aspect ratio (Aspect Ratio is the ratio of the largest dimension to the smallest dimension of the particle) the aspect ratio ranges from unity (for spherical particle) to about 10 for flake-like or needle-like particle

7. Particle Shapes in Metal Powders

8. SEM photo of iron powder particles made by atomisation Ni- based super alloy powder particles made by the rotating electrode process

9. Pure Metals Alloys Compunds Aluminium Aluminium-iron Borides(chromium, tungsten, etc.) Antimony Brass Carbides (molybdenum, tungsten, etc.) Bismuth Copper-zinc-nickel Molybdenum disulphide Cadmium Nickel-chromium-iron Nitrides (silicon titanium, etc.) Copper Nickel-copper Zirconium hydride Iron Nickel-iron Lead Silicon-iron Tin Stainless steel Titanium Vanadium zinc Widely used Metal Powders

10. Methods of Powder Production

11. Atomization Molten metal is forced through a nozzle into a stream of air or water, upon contact with the stream the molten metal is solidified into particles of wide range of sizes The size of he particles formed depends on the temperature of the metal, rate of flow, nozzle size and the jet characteristics

12. Reduction the reduction of metal oxide, removal of oxygen, uses gases such as hydrogen and carbon monoxide as reducing agents, very fine metallic oxides are reduced to metallic state, the metals produced by this metal by this method are spongy and porous, and have uniformly sized spherical or angular shapes. important points here are the metals produced by this method are spongy and porous, as well as they are uniformly sized

13. Carbonyls metal carbonyls such as iron carbonyl and nickel carbonyl, are formed by letting iron or nickel react with carbon monoxide. The reaction products are then decomposed to iron and nickel, they turn into small, dense, uniform, spherical particles of high purity Again here, we can see the emphasis is on the shape and size of the particles

14. Roll Crushing Ball Milling Hammer Milling

15. Mechanical Alloying In mechanical alloying powders of two or more metals are mixed in a ball mill, under the impact of hard balls, the powder fracture and join together by diffusion forming alloy powders when the final product has some specification regarding the mechanical and the physical property, we need to blend the different metals together to get the final property. So, we need to go for this process

16. Electrolysis here the basic principle is to pass high amperage through metal plates acting as anode and cathode in the presence of electrolyte. t he powdery deposit on the cathode is scraped off and pulverized to produce the powder of desired grain size s o, we do not get the metal powder to be directly used, whatever is deposited on the cathode, we remove that and then we pulverize it

17. Blending Metal Powders Powders made by various processes have different sizes and shapes, they must be mixed to obtain uniformity Powders of different metals and other materials can be mixed to impart special physical and mechanical properties and characteristics to the P/M part Lubricants can be mixed with powders to improve their flow characteristics, the results are reduced friction between the metal particles, improved flow of the metal powders into the dies, and longer die life with less wear

18. Blending … Powder mixing must be carried out under controlled conditions, to avoid deterioration or contamination Deterioration is caused by excessive mixing, which may alter the shape of the particles and work harden them and making the subsequent compaction difficult Powders can be mixed in air, in inert atmospheres (to avoid oxidation), or in liquids, which act as lubricants and make the mix more uniform

19. Hazard with Metal Powders Because of their high surface are-to-volume ratio, metal powders are explosive Al, Mg, Ti , Zr , and Th are particularly explosive Great care must be exercised both during blending and in storage and handling Precautions include preventing sparks, open flames and chemical reactions

20. Compaction Application of high pressure to the powders to form them into the required shape. Conventional compaction method is pressing , in which opposing punches squeeze the powders contained in a die. The work part after pressing is called a green compact , the word green meaning not yet fully processed. The green strength of the part when pressed is adequate for handling but far less than after sintering.

21. Press powder into the desired shape and size in dies using a hydraulic or mechanical press Pressed powder is known as “green compact” Stages of metal powder compaction: Compacting

22. Compacting Powders do not flow like liquid, they simply compress until an equal and opposing force is created. This opposing force is created from a combination of resistance by the bottom punch and friction between the particles and die surface Compacting consolidates and dandifies the component for transportation to the sintering furnace. Compacting consists of automatically feeding a controlled amount of mixed powder into a precision die, after which it is compacted .

23. Compacting Compacting is usually performed at room temperature. Pressures range from 10 tons per square inch (tons/in 2 ) (138 MPa) to 60 tons/in 2 (827 MPa), or more.

24. Figure: (Left) Typical press for the compacting of metal powders. A removable die set (right) allows the machine to be producing parts with one die set while another is being fitted to produce a second product .

25. Compaction Sequence Figure: Typical compaction sequence for a single-level part, showing the functions of the feed shoe, die core rod, and upper and lower punches. Loose powder is shaded; compacted powder is solid black.

26. Sintering It is a process whereby green compacts are heated in a controlled atmosphere furnace to temperature below the melting point , but sufficiently high to allow bonding of individual particles. The principle variables in sintering are temp. , time , and the furnace atmosphere. Temperature is around 70-90% of the melting point of metals and alloys. Time ranges from 10 min.(iron and copper alloys) to 8 hours(tungsten and tantalum).

27. Sintering temperature and time MATERIAL TEMPERATURE (K) TIME (Min) Copper , brass , bronze 1030-1160 10-40 Nickel 1270-1420 30-45 Stainless steels 1370-1560 30-60 Ferrites 1470-1770 10-600 Molybdenum 2273 120 Tungsten 2630 480 Tantalum 2670 480

28. Secondary and Finishing Operations In order to improve the properties of sintered P/M products further or to impart special characteristics several additional operations may be required, like : Coining and Shaping are compaction operations, performed under high pressure to impart dimensional accuracy, to improve strength and surface finish by densification .

29. Impact forging It is done for good surface finish, good dimensional tolerances , and a uniform and fine grain size. Impregnating The typical application is to impregnate the sintered part with oil ,usually by immersing the part in heated oil, such components have a continuous supply of lubricant, by capilary action, during their service lines.

30. Infiltration A slug of lower melting point is placed against a sintered part and then the assembly is heated to a temperature sufficient to melt the slug. The molten infiltrates the pores, by capillary action to produce a relatively pore free part having good density and strength(infiltration of iron based compacts by copper) The hardness and tensile strength is improved and the pores are filled, which prevents moisture penetration.

31. Plating It is given for pleasing appearance and protection from corrosion, inner porosity has to be taken care of before plating and has to be eliminated. Impregnation with molten metal helps, but galvanic corrosion is likely between dissimilar metals. Difference in coefficients of expansion and contraction may lift the plating material. Impregnating the part with a plastic resin will overcome most of these difficulties.

32. Machining Certain features such as threads, grooves, side holes and undercuts are machined on the semi finished sintered blanks. High speed steel tools prove satisfactory for short runs whereas tungsten carbide tools are recommended for machining for a longer time. Volatile coolants such as carbon tetrachloride can be used because they vapourize readily and leave no residue. Coolant oil of some type as used to impregnate a self lubricating bearing can also be used.

33. Design considerations for P/M The shape of the part must permit easy ejection from die. The shape must not require the poeder to flow into thin walls, narrow passages or sharp corners. The shape of the part must permit the construction of stong and rigid tooling. Several stepped diameters should be avoided. Abrupt changes in sections and internal angles without generous fillets should be avoided,

34. Powder Metallurgy products The products can be classified commonly into four groups: Porous products , bearings and fillers Products of complex shapes that require considerable machining, like gears Products made from materials that are very difficult to machine, tungsten carbide Products where the combined properties of two metals, or of metals and non metals are desired

35. Applications Metal Filters Used for filtering, diffusing, controlling the flow of gases and liquid , separating liquid having different surface tensions, removing moisture from airstreams, acting as sound deadeners etc. Cutting tools and Dies Cemented carbide cutting tool inserts are widely used in machine shops, produced by p/m from tungsten carbide powder mixed with cobalt binder, these cutting tools have high hot hardness and wear resistance.

36. Bearings and bushes Used with rotating parts , made from copper powder mixed with graphite, lead and tin are used for better wear resistance, after sintering the bearings are impregnated with oil, porosity in the bearings may be as high as 40% of the volume , the lubricant is metered to the bearing surface by capillary action when heat or pressure is applied. Structural or Machine parts Machine parts including gears, sprockets and rotors are made from metal powders mixed with sufficient graphite to give the product desired carbon content, the parts usually have 20% porosity, self lubrication helps in quite operation and lower wear.